Regulator control circuit and method

ABSTRACT

Switching devices control the rectification and flow of alternating current power from a source such as an alternator to a load such as a battery in response to both the voltage of the battery and a minimum selected time period that is selected to eliminate or reduce an imbalance between various phases or polarities in possible current carrying paths. The selected time period may be constant or a predetermined function of variables such as the speed of the alternator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/422,717, filed Oct. 31, 2002, the disclosure of which is herebyincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of electrical regulators and,in particular to solid state switching thereof.

BACKGROUND OF THE INVENTION

Outboard motors and recreational vehicles such as snowmobiles often haveelectrical systems including a permanent magnet alternator, a battery,various connected loads, and a solid state combination regulatorrectifier to change the alternating current output of the alternator toa controlled DC current for maintaining the required charge on thebattery. As these vehicles have become more sophisticated, the requiredelectrical loads have in general increased and there has been acorresponding requirement to increase the current carrying capability ofthe regulators and increase the amount of current obtainable from agiven size or weight alternator. Except in some very low powerapplications, the regulators are in general full wave rectification fromeither single phase or three phase permanent magnet alternators.Improvements in the alternator output have come recently from suchtechnology as rare earth magnets. This has resulted in many alternatorwindings running near the upper limit of a temperature capability of theinsulation systems of the magnet wire. Regulators commonly used in thistype of system include solid state switches, such as silicon controlrectifiers and diodes, used to control the current flow from thealternator to the battery and load. These components and the alternatorwinding must of course be sized so that when the alternator is producingfull output, with the switching devices such as silicon controlrectifiers always on when instantaneous circuit polarity is such thatthey can conduct, that both the alternator and the semi conductorcomponents are within their current capabilities, or stated another waywithin the temperature capabilities of those components. A problemarises if the design of the regulator allows an imbalance in currentbetween the various phases of a three-phase alternator or the positiveand negative half cycles of a single-phase alternator.

It has been observed that a full wave rectified single phase alternatoroperating at high RPM can maintain as much, and in some cases evenslightly more, average current output with one of the polaritiesdisabled. In this extreme example, even though the average current tothe battery and load remains approximately the same the average currentthrough the switching device and diode that is still in operation isincreased 2 to 1 and the true RMS current or effective heating value ofthe current through the alternator winding is also drasticallyincreased. The forgoing results from an effective phase shift, resultingin conduction of greater than 180 degrees compared to the open circuitvoltage waveform of the alternator. Whether a given combination ofalternator and regulator operates with a reasonable balance between thepossible conducting paths, i.e. polarity or phases, can be influencedgreatly by the connected load and the condition or type of battery used.Typically, the manufacturer of a vehicle cannot control the load and thebattery condition. Thus, even if initial testing indicated thatcomponents share loads as desired it is often found in vehicles at alater time, particularly where batteries may have been substituted orthe original battery type deteriorated, that a severe imbalance in theload occurs between for instance the positive and negative half cycle ofa full wave rectified single phase, or between the phases of a threephase alternator.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a control circuit or methodfor minimizing or eliminating the above referenced imbalance betweenvarious current carrying paths, but at the same time minimizing theeffective pulsation in the current supply to the load and battery. Thismay be done by controlling the operation of the solid state switches notonly based on the voltage across the load or battery but also based on apre-determined gating time and sequence of the switching elements orsilicon control rectifiers in the various conducting paths in theregulator rectifier.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will become more apparent byreferring to the following detailed description and drawings in which:

FIG. 1 is a combination circuit diagram and block diagram of oneembodiment including a permanent magnet alternator A1 shown as a singlewinding is connected through rectification and switching components SCR1SCR2 and D1 and D2 to a load consisting of battery B1 switch S1 and loadresistor L1;

FIG. 2 is a graph of average output current obtainable from thealternator and SCR-diode bridge in FIG. 1, plotted vs. RPM or speed ofthe alternator;

FIG. 3 is an alternate embodiment of FIG. 1 including a three-phasealternator, wherein the alternator is represented as 3 inductivewinding, in a delta configuration, with an understanding that otherconnections such as the three phases Y or various other numbers ofphases may be substituted by one skilled in the art within the spiritand teaching of this application, and wherein the three-phaseapplication imbalance in current may arise with either 1 or 2 of theSCR's always on and the remaining 2 or 1 always off, wherein such may beextreme examples realizing that any amount of imbalance can occur shortof the current through a possible current path actually being zero; and

FIG. 4 illustrates three wave forms that are all synchronized with eachother, that is with the mechanical rotation of the alternator shaft,which may be typical of an alternator and rectification scheme asdescribed with reference to FIGS. 1 and 2, wherein the bottom curverepresents an open circuit voltage of the alternator, the middle curverepresents an instantaneous value that is plotted as an average for thehalf wave curve in FIG. 2, and the top curve represents an instantaneousvalue full wave rectified that is plotted as an average for the fullwave curve of FIG. 2, and wherein the data shown in FIGS. 2 and 4represent actual values from a production alternator used on a smallrecreational vehicle, and herein provided as examples, but in no way areto be construed as restrictive to the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Primenotation is used to indicate similar elements in alternate embodiments.

With reference to FIGS. 1 and 3, the solid state switching elements SCR1and SCR2 are shown as controlled by two circuits shown in a blockdiagram form. The first being a voltage sense circuit connected to theload and the second being a switch control circuit responsive to thevoltage sense circuit to generate control or gate signals for thecomponents SCR1 and SCR2. The voltage sense circuit derives its inputfrom a voltage input connected to the battery positive terminal and aground connected to the battery negative terminal. Internally thevoltage between these terminals is compared to a reference to determineif a battery voltage is above or below the desired level and the outputstate is changed accordingly. The voltage sense circuit may also containan over voltage detection circuit which will function, in the case of avoltage greatly above the desired level, to shut down the output for aselected interval. This would be desirable for instance if a batterylead became disconnected. By way of example, the voltage sense circuitmay be made sensitive to either the average or the instantaneous valueof the battery voltage. Sensing the instantaneous value maximizes theeffect of battery lead and battery internal impedances. Batterytemperature may also be sensed and used to modify the voltage set point.The switch control circuit responds to the output of the voltage sensecircuit and may have additional inputs, such as a frequency inputconnected to the alternator, and a circuit responsive to the temperatureof a selected portion of the regulator so as to reduce or disable theoutput under an over temperature condition. In previously knowncircuitry the output of the switch control circuit needed to be onlylong enough to turn on the switching devices such as the SCR shown. Forembodiments of the present invention, herein described by way ofexample, this portion of the circuit includes means of creating longeroutput pulses capable of turning on the various switching devices orsilicon control rectifiers in a desired sequence over a desired time.The switch control circuit will have internal timing functions tominimize, as will be presently described, any imbalance between thecurrents handled by SCR1 and SCR2. With continued reference to FIGS. 1and 2 and in accord with one embodiment of the present invention, theRMS value of the current through the alternator Al and thesemiconductors D1, D2, SCR1 and SCR2 is determined at engine maximumRPM. These provide the RMS values that make up F2 of FIG. 2. A speed,shown as RPM1 of FIG. 2, may then be determined such that below RPM1, inthe half wave, or maximum imbalance condition, all component RMScurrents are below the maximum values balanced at maximum RPM. AboveRPM1, at least one RMS value from maximum RPM balanced values isexceeded. RPM1 may be increased if all components are known to operatebelow maximum temperature or ratings at maximum engine RPM.

For the single phase system shown in FIG. 1, the time required would beequal to, or slightly greater than one half the period of the opencircuit wave form at RPM1. In the simplest embodiment of this invention,this time period could be fixed regardless of RPM. A first level ofrefinement would be for this pulse duration to be created only at speedsabove RPM1. Further refinement would be for the half cycle duration tobe automatically applied on a basis computed from the speed of thealternator at that particular instant. The level of refinement necessarywould be determined by available safety factors in components and thedegree of ripple of fluctuation in the battery voltage that wasallowable. Gating on the switching devices for longer than necessarywill in general produce higher ripple voltage at the battery terminals.In the three-phase circuit of FIG. 3 the pulse duration being one halfof the electrical cycle, would be determined by the number of phases andjust sufficient to assure that the conducting paths of all phases wereturned on following the initiation by the voltage sense circuit of theturn on of any conducting path.

For the purpose of discussion with reference to FIG. 2, two conditionsare assumed. The first condition is that gate signals are supplied toboth SCR1 and SCR 2 whenever the voltage across them is of the polaritywhere they can conduct. This curve is labeled full wave. The secondcurve assumes that a gate signal is always supplied to SCR 1 wheneverthe polarity across it is such that it could conduct and that a gatesignal is never supplied to SCR 2. The resulting curve is labeled ashalf wave. The RPM scale on FIG. 2 shows an engine idle RPM and maximumRPM. These should be understood to be the characteristics of an enginemechanically driving the alternator A1 illustrated with reference againto FIG. 1.

1. A voltage regulator circuit comprising: an alternator driven at avariable speed; a source of AC power operable with the alternator; a DCload connected for receiving the power; and at least two switchablerectifying means to rectify and control the flow of power from thealternator to the load, wherein the at least two switchable rectifyingmeans each include input control means, and wherein the input controlmeans is responsive to the voltage of the DC load, and also responsiveto a timing pulse of selected duration, the duration chosen to insurethat following a signal to an input control means responsive to avoltage of the DC load, that all other switchable rectifying means areswitched on for a next conduction cycle if the variable speed is above aselected level.
 2. The circuit of claim 1, wherein the selected durationis a function of the variable speed.
 3. The circuit of claim 1, whereinthe selected duration decreases with the variable speed when thevariable speed is above the selected level.
 4. The circuit of claim 1,wherein the input control means is responsive to an instantaneousvoltage value of the DC load.
 5. The circuit of claim 1, wherein theinput control means is further responsive to temperature.
 6. The circuitof claim 5, wherein the temperature is a temperature within the voltageregulator circuit.
 7. The circuit of claim 5, wherein the temperature isrelated to a temperature of a battery operable with the voltageregulator circuit.
 8. The circuit of claim 5, wherein the voltageregulator circuit is sensitive to both a temperature thereof and atemperature of a battery operable therewith.